发行人:黄升龙所长    编辑委员:蔡睿哲教授    主编:林筱文    发行日期:2008.10.03

最新消息与活动公告    所务公告及活动花絮    迈向顶尖大学计划研究成果专栏

光电所博士班应届毕业生研究成果专栏    光电要闻

最新消息与活动公告

 

   本所10月份演讲公告:

日期

讲者简介

讲题

地点

时间

10/3 (Fri)

Prof. François Ladouceur

Photonics Group at the University of New South Wales

Photonics Material Research at the University of New South Wales

博理馆

101演讲厅

14:30-16:30

 

所务公告及活动花絮

 

光电所所学会2008学年度羽球赛花絮

(时间:2008年9月8日;地点:台湾大学新体育馆3F)

花絮整理:所学会会长刘光中

       今年的光电所羽球大赛,于九月八日下午盛大举行了。这次参加的队伍共有8队,人数达到48人。在经过了三个小时的循环对战后,由第四队取得本次大赛的冠军,另外第二、三、六、七队积分相同,并列亚军。比赛之余还有不少同学虽然没有来得及报名,但也到场利用场地闲暇之际与大家一同运动,鼓励大家多多运动正是本次羽球大赛举办的宗旨所在。本次大赛圆满落幕,在切磋球技、交流感情之际,希望大家也能够忘怀输赢,并且再次满怀着热情,踊跃参加下一次的光电所体育活动。

参赛同学热身中 跳杀

肚子也入镜了

虽然穿着皮鞋依然奋勇作战

学妹们也参加羽球赛 冠军队伍合照

本届赛事最强选手

场边休息时合照

 
 
 

迈向顶尖大学计划研究成果专栏

 

Low-Actuation-Voltage MEMS for 2-D Optical Switches

Hsin-Ta Hsieh and Prof. Guo-Dung John Su

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所苏国栋教授

 A novel MEMS fabrication process was developed to integrate vertical stress-free micromirrors and electromagnetic actuators without an extra assembly process. The size of the TMAH etched micromirror is 20 μm × 500 μm × 1200 μm, which is large enough to ensure low insertion loss for 2-D optical-switching applications. The surface roughness of the micromirror is measured to be as low as 20 nm by the white light interferometer, which typically results in 0.2-dB optical loss. The center-aligned vertical mirror showed an excellent TDL of 0.05 dB. An appropriate magnetic circuit design reduces the actuation voltage to 0.5 V with a power consumption of about 3.5 mW. A reasonable fast-switching time of 5 ms can be achieved by eliminating the resonant-frequency components of the MEMS switch through edited waveforms. Long-term cycling and mechanical reliability tests proved that the proposed MEMS optical switch can pass the rigorous requirement of optical communications. The PDL and WDL are both less than 0.1 dB.

 

(a) Operated device and  (b) applied voltage versus normalized coupling efficiency and moving heights.

Stress analysis for corner design effect.

Switching time of a 2-D MEMS switch.

Schematic drawing of a 4 × 4 MEMS optical switch with periodical magnet ribbons.

 

 

 

 

Finite-Difference Modeling of Dielectric Waveguides with Slanted Facets

Y.-P Chiou, Y.-C. Chiang, C.-H. Lai, C.-H. Du, and H.-C. Chang

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所邱奕鹏教授

  Abstract -- With the help of an improved finite-difference (FD) formulation, we investigate the propagation characteristics of a slant-faceted polarization converter. The formulation is full-vectorial and it takes into consideration discontinuities of fields and their derivatives across the abrupt interfaces. Hence, the limitations in conventional FD formulation are alleviated. Field behaviors across the slanted facet are incorporated in the formulation and hence the staircase approximation in conventional FD formulation is removed to get better modeling of the full-vectorial properties.

 

 One limitation of conventional finite-difference method is that grids in the computation are normally parallel to the axes in the discretization of field components. Staircase approximation is often required when the fields are cross a slanted interface between two different materials. The convergence is slow due to the staircase approximation as compared to other methods without staircase approximation, e.g. finite-element method. In addition, the full-vectorial properties may not be accurately modeled under such approximation. To get rid of such limitation, our improved finite-difference method is adopted.

 

 The investigated structure is shown in Fig.1. An x-polarized field is launched from a standard input waveguide (IW). This incident field excites both the first and second hybrid modes of nearly equal modal amplitudes. As these two hybrid modes propagate along the polarization rotating waveguide (PRW), they would become out of phase at the half-beat length and their combined modal fields produce mainly a y-polarized field in the following output waveguide (OW). The polarization rotating waveguideis based on a rib waveguide with one side wall slanted at an angle around 45 degrees.

 

 In the structure, both hybrid modes have comparable field components in x- and y- directions, and their polarizations are no longer mainly in the x- or y- direction but in the direction parallel or perpendicular to the slanted wall. As shown in Fig.2, the field is periodically converted between x- and y- polarizations. To verify our simulation, finite-element method (FEM) and Yee-mesh-based finite-difference beam propagation method (Yee-FD-BPM) are adopted as shown in Table I. Both electrical and magnetic fields are used at the same time in the formulation of Yee-FD-BPM. Different methods show very good agreement. Furthermore, we also use conventional finite-difference scheme with staircase approximation and index-average approximation to calculate the same problem. We find that the hybrid modes can not be correctly obtained either by our codes or by commercial software. The fundamental modes may become x- or y-dominant modes, not as expected. To sum up, our improved finite-difference scheme can easily handle structures with facets that are not parallel to x- or y-axis, which alleviates the limitation in conventional finite-difference method.

 

Fig.1 (a) Polarization converter (b) Cross-section view.
 

Fig.2 Power in x- (solid line) and y- (dashed line) polarized fields along the propagation.

 
Table I

 

 

 

 

 

Design and Analysis of Compact Slot Waveguide Directional Coupler-Based Polarization Splitter on Silicon-on-Insulator

Professor Ding-wei Huang

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所黄鼎伟教授

 A slot waveguide directional coupler-based polarization splitter on SOI which exhibits excellent polarization splitting behavior for optical signals around 1.55 mm is designed and analyzed. In our design, the silicon photonic wire is covered by air (nc = 1) and patterned on the buried oxide layer (ns = 1.444) of the SOI wafer, where the low-refractive-index region (slot region) is sandwiched by high-refractive-index silicon (nr = 3.474) at 1.55 μm as shown in Fig.1. The schematic layout of the entire device is shown in Fig. 2. The width w and height h of each photonic wire at the slot region is chosen to be 0.21 μm and 0.25 μm; while the width of the slot ws is set to be 0.2 μm due to the limitation of the fabrication capability. The propagation of light in the directional coupler can be expressed in terms of even and odd modes with effective indices ne and no, which are functions of the waveguides spacing g as shown in Fig. 3. By carefully choosing the spacing g (g = 0.48 μm) between the two waveguides, the coupling length of TE mode LTE can be twice that of TM mode LTM, i.e. LTE /LTM = 2. Meanwhile the length of the coupling region of the device is chosen to be L = 2LTM = LTE, thus the two modes can be successfully separated into 2 different output ports. By using FDTD technique, the electric field intensities of the TE- and TM-polarized modes propagating in the device can be calculated as shown in Fig. 4.

 

Fig. 1 A cross-sectiional view of slot directional coupler-based polarization splitter. Fig. 2 Schematic layout of the entire device.

Fig. 3 Effective indexes of even modes ne and odd modes no induced in TE polarization (neTE, noTE) and TM polarization (neTM, noTM) of a coupler as a function of waveguide spacing g. Fig. 4 Polarization splitting behavior in the device. The left-hand side is the result of TM mode and the right-hand side is the result of TE mode.

 

 

光电所博士班应届毕业生研究成果专栏

 

论文题目:光学同调断层扫瞄技术于口腔癌诊断之研究

姓名:蔡孟灿

指导教授:杨志忠教授

摘要

口腔癌在台湾男性癌症排名第四,对于一般口腔癌病患,早期诊断可高达百分之七十五的五年以上存活率。光学同调断层扫瞄技术可以提供纵切面的组织造影,并具有高解析、高造影速度以及较深的造影深度(2~3 mm)等优点,因此光学同调断层扫瞄技术适合作为口腔癌早期诊断的工具。在这研究中,我们应用光学同调断层扫瞄技术于离体以及临床的口腔癌研究。我们建立了一套扫频式的光学同调断层扫瞄系统,首先针对从口腔癌病患身上切除的口腔癌样本做扫瞄。这套系统具备8 μm的纵向分辨率以及灵敏度可达108 dB,透过这套系统扫瞄,可区分出正常以及癌组织。

在临床上,我们将此扫频式的光学同调断层扫瞄系统接上一特别设计的扫瞄探头,在医院针对口腔癌前病变和口腔癌病患扫瞄,并统计上分析有效的诊断指标。在这部分,我们提出了三种指标,其中包含纵向强度分布的标准差、由纵向强度分布的空间频域频谱所得到的指数衰减常数(a),以及当上皮层和结缔组织间的接口仍存在时,所得到的上皮层厚度。另外,我们分析在统一标准和个别相对标准下,这些诊断指标的灵敏度以及明确度。由结果发现,针对中度上皮变异以及鳞状细胞癌,标准差以及a值将会是很好的诊断指标。另一方面,上皮层厚度适合用作上皮增生以及中度上皮变异诊断上的指标。另外,我们也利用此可携式的扫频式光学同调断层扫瞄系统来追踪评估口腔癌病患经由光动力疗法治疗后其复原情形。我们将列出其中两位病患治疗后的结果,并藉由上述三种诊断指针来分析光学同调断层扫瞄系统的扫瞄结果。

 

 

光电要闻

 

— 数据提供:影像显示光电科技特色人才培育中心.影像显示科技知识平台 —

— 整理:林晃岩教授、陈冠宇 —

 

IBM开发出采用磁性材料与利用自旋电子学技术之超高密度非挥发性内存

 美国IBM与台湾的工业技术研究院(ITRI)宣布,将合作研发采用磁性材料的非挥发性内存“Racetrack Memory”Racetrack MemoryIBM公司阿尔马登研究中心(Almaden Research Center)的Stuart ParkinIBM院士)所提出的新型超高密度非挥发性内存。

 

 IBMITRI的共同研究小组将探索Racetrack Memory所用的新材料及新构造。ITRI的副院长Ian Chan表示:「透过在多个候选对象中找出最适合Racetrack Memory的材料及构造,可从中得到新的知识。」

 

 美国IBM发表的新型非挥发性内存“Racetrack Memory”是基于自旋电子学(Spintronics)技术,同时具备高存取性能且强固(理论上摔不破)等「半导体内存」的优点以及成本低、容量大等「硬盘」的优点。IBM表示,使用Racetrack Memory,可在随身装置上储存50万首乐曲或3500部电影,这相当于现有随身硬盘可储存容量的约100倍。

 

 Racetrack Memory采用记录在磁性材料中的位列(Bit Column),像赛车跑道那样排列的构造。因沿垂直或水平于硅底板方向配置的磁性材料可大量记录信息,且数据在轨道上跑(the data "races" around the wire "track"),所以不会有移动的读取装置,因此更耐用、发热更低且更省电(一个电池可以读取一个星期,且不通电时数据可保存十年)。而且既然使用电子的自旋来储存数据,重复多次的读取也不会耗损,理论上可以做无限次读取。

 

 Racetrack Memory与以往的半导体内存相比的优点,是能够以更小的芯片面积实现大容量。IBM院士Stuart Parkin表示:采用沿硅底板垂直方向配置磁性材料的构造,在理论上可以同时读取10~100个左右的位(bits)。即沿垂直方向层迭了约100个由磁性材料形成的位。这种情况下,磁性材料由物理分割划分的约100个区域构成,各区域按照磁化方向对信息“1”“0”进行记录。

 

 Racetrack Memory上,向磁性材料的位列施加电流脉冲后,可利用分割内存地址的磁壁(magnetic domain walls)发生移动的现象。经过改变脉冲数,可实现对特定地址的随机访问。访问特定地址之后可执行数据的读写。此次试制出了包含多个磁壁的磁性材料,并确认能够利用磁壁移动对访问对象的内存地址进行选择、读取、写入。

 

图:Racetrack Memory的结构

 

 

参考数据:

“Current Controlled Magnetic Domain-Wall Nanowire Shift Register,” Science, Vol. 320, no. 5873, pp. 209 – 211, 11 April 2008.

 

原厂发布资料:

http://www-03.ibm.com/press/us/en/photo/23860.wss

http://www-03.ibm.com/press/us/en/pressrelease/23859.wss

 

参考中文数据:

http://big5.nikkeibp.co.jp/china/news/semi/semi200804220118.html

 

 

 

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